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November 2, 2005

First Starlight Possibly Detected

by Sam Savage

MILWAUKEE, Wisconsin (AP) -- Researchers from NASA's Goddard Space Flight Center in Maryland believe they have captured traces of radiation from long-extinguished stars that were "born" during the universe's infancy.

The research represents the first tangible -- but not conclusive evidence of these earliest stars, which are thought to have produced the raw materials from which future stars, including our sun, were created.

The Big Bang, the explosion believed to have created the universe, is thought to have occurred 13.7 billion years ago. About 100 million years later, hydrogen atoms began to merge and ignite, creating brightly burning stars. Just what these stars were like wasn't clear.

"Where they lived, how big they were, how much light they emitted, whether they even existed, we weren't sure," said astrophysicist Alexander Kashlinsky, the lead author of the article appearing in Thursday's issue of the journal Nature. "What we've done, we think, is obtain the first information about these stars."

Kashlinsky's team used NASA's Spitzer Space Telescope to measure the cosmic radiation, which is infrared light invisible to the human eye, in a small sliver of the sky. The team then subtracted the radiation levels of all known galaxies and suggested that the leftover measurements include radiation given off by those earliest stars.

The exercise was like taking a recording of a stadium full of loud people and subtracting the noise of every person except one to hear the voice of that single individual.

If the team's conclusions are correct, the study will advance understanding of how the universe originally lit up.

Avi Loeb, a Harvard astronomy professor who was not involved in the research, said the early universe was probably dark for half a million years. Later, hydrogen coalesced into brightly burning stars that were hundreds to a million times more massive than the sun, and these are the stars whose fingerprints Kashlinsky's team hopes it has found.

"That's why this (study) was so exciting -- for the first time, we're looking at potential evidence of how the first starlight was produced and when it was formed," Loeb said.

An astronomy professor at the California Institute of Technology who was not involved in the study cautiously agreed with Kashlinsky's conclusion. In a commentary published by Nature, Richard Ellis wrote, "Even a minor blunder in removing these foreground signals might lead to a spurious result," but he said in an interview that Kashlinsky's team did the best job it could given the constraints of the technology used.

"I can't find anything wrong with the analysis. Of course, the next step is for other astronomers to try to prove it right," Ellis said.

Ned Wright, an astronomy professor at UCLA, was more doubtful. He argued that the process of removing the radiation contribution of other stars is too imprecise to make the team's conclusions valid, and that the measurement it saw is not the signal of ancient stars.

"I'm very skeptical of this result. I think it's wrong," he said. "I think what they're seeing is incompletely subtracted residuals from nearby sources."

Loeb agreed that Kashlinsky's results were not irrefutable, but he said the team's conclusion is a plausible first step that represents an important milestone toward understanding how stars first formed.

In the same issue of Nature, a team of Chinese researchers reported on a separate astronomical issue.

They said they had found that the super-massive black hole at the center of the Milky Way is small enough that it would fit between the Earth and the sun. That puts it at half the size of previous estimates.